Slicker, simpler, simpler, flatter, fuller, foxier theme.
To revert the browser to its default tab closer behavior, add this line to your userchrome.css:
.tabbrowser-tabs[overflow="true"] .tabbrowser-tab:not([selected="true"]) .tab-close-button { display: none !important;}
To remove all tab closers, all the time, add this line:
.tabbrowser-tabs .tab-close-button { display: none !important;}